METHOD OF SPECKLE-NOISE PATTERN REDUCTION AND APPARATUS THEREFOR BASED ON REDUCING THE TEMPORAL-COHERENCE OF THE PLANAR LASER ILLUMINATION BEAM BEFORE IT ILLUMINATES THE TARGET OBJECT BY APPLYING TEMPORAL PHASE MODULATION TECHNIQUES DURING THE TRANSMISSION OF THE PLIB TOWARDS THE TARGET
First Claim
1. A method of reducing speckle-pattern noise at the image detection array of a planar laser illumination and imaging (PLLIM) based camera system, said method comprising the steps of:
- (a) producing a planar laser illumination laser beam (PLIB) within a planar laser illumination and imaging (PLIIM) based system including an image detection array having image forming optics with a field of view (FOV) arranged in a coplanar relationship with said PLIB;
(b) reducing the temporal-coherence of said planar laser illumination beam (PLIB) before said PLIB illuminates a target object, by applying a temporal phase modulation technique during the transmission of said PLIB towards the target, so that the object is illuminated with a temporally coherent-reduced planar laser illumination beam (PLIB) and numerous substantially different time-varying speckle-noise patterns are produced at said image detection array over the photo-integration time period thereof;
(c) detecting said numerous substantially different time-varying speckle-noise patterns over said photo-integration time period; and
(d) temporally averaging said detected speckle-noise patterns at said image detection array during said photo-integration time period thereof, thereby reducing the RMS power of observable speckle-noise patterns at said image detection array.
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Abstract
A planar laser illumination and imaging (PLLIM) based camera system capable of producing digital images with reduced levels of speckle-pattern noise. The PLIIM based camera system comprises a planar laser illumination array (PLIA) including a plurality of laser diodes for producing and projecting a planar laser illumination beam (PLIB), so as to illuminate an object as it is moving past said PLIIM based camera system. An image formation and detection (IFD) module is provided having a image detection array and imaging forming optics for providing the image detection array with a field of view (FOV). The PLIB and FOV are arranged in a coplanar relationship along the working range of the PLIIM based camera system so that the PLIB illuminates primarily within the FOV of the IFD module. A speckle-pattern noise reduction subsystem is integrated with the PLIA, for reducing the temporal-coherence of said planar laser illumination beam (PLIB) before the PLIB illuminates a target object. The speckle-pattern noise reduction subsystem carries out a temporal phase modulation technique during the transmission of the PLIB towards the target, so that the object is illuminated with a temporally coherent-reduced planar laser illumination beam (PLIB) and numerous substantially different time-varying speckle-noise patterns are produced at the image detection array over the photo-integration time period thereof. The numerous substantially different time-varying speckle-noise patterns are detected at the image detection array over the photo-integration time period, and the detected speckle-noise patterns are temporally averaged at said image detection array during the photo-integration time period thereof. As a result of such temporal averaging, the RMS power of observable speckle-noise patterns is reduced at the image detection array. By virtue of the present invention, it is now possible to enjoy the benefits of using laser-based illumination during high-speed imaging operations, without the adverse effects associated with speckle-pattern noise.
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Citations
12 Claims
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1. A method of reducing speckle-pattern noise at the image detection array of a planar laser illumination and imaging (PLLIM) based camera system, said method comprising the steps of:
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(a) producing a planar laser illumination laser beam (PLIB) within a planar laser illumination and imaging (PLIIM) based system including an image detection array having image forming optics with a field of view (FOV) arranged in a coplanar relationship with said PLIB;
(b) reducing the temporal-coherence of said planar laser illumination beam (PLIB) before said PLIB illuminates a target object, by applying a temporal phase modulation technique during the transmission of said PLIB towards the target, so that the object is illuminated with a temporally coherent-reduced planar laser illumination beam (PLIB) and numerous substantially different time-varying speckle-noise patterns are produced at said image detection array over the photo-integration time period thereof;
(c) detecting said numerous substantially different time-varying speckle-noise patterns over said photo-integration time period; and
(d) temporally averaging said detected speckle-noise patterns at said image detection array during said photo-integration time period thereof, thereby reducing the RMS power of observable speckle-noise patterns at said image detection array. - View Dependent Claims (2, 3, 4, 5, 6)
modulating the temporal phase of the transmitted PLIB along the planar extent thereof according to a temporal phase modulation function (TIMF) so as to modulate the temporal phase along the wavefront of the PLIB and produce said numerous substantially different time-varying speckle-noise patterns at the image detection array during the photo-integration time period thereof.
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3. The method of claim 1, wherein the temporal phase modulation technique practiced during step (b) is selected from the group consisting of:
- using an optically-reflective cavity (i.e. etalon device) affixed to external portion of each VLD;
using a phase-only LCD temporal intensity modulation panel; and
using a fiber optical array.
- using an optically-reflective cavity (i.e. etalon device) affixed to external portion of each VLD;
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4. The method of claim 1, wherein step (b) comprises using the planar laser illumination beam is temporal phase modulated prior to target object illumination employing photon trapping, delaying and releasing principles within an optically reflective cavity (i.e. etalon) externally affixed to each visible laser diode within the planar laser illumination array.
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5. The method of claim 1, wherein the planar laser illumination beam (PLIB) is temporal phase modulated using a phase-only type LCD-based phase modulation panel prior to target object illumination.
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6. The method of claim 1, wherein the planar laser illumination beam (PLIB) is temporal phase modulated using a high-density fiber-optic array prior to target object illumination.
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7. A planar laser illumination and imaging (PLLIM) based system capable of producing digital images with reduced levels of speckle-pattern noise, said PLIIM based camera system comprising:
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a planar laser illumination array (PLIA) including a plurality of laser diodes for producing and projecting a planar laser illumination beam (PLIB) so as to illuminate an object as it is moving past said PLIIM based camera system;
an image formation and detection (IFD) module having a image detection array and imaging forming optics for providing said image detection array with a field of view (FOV), wherein said PLIB and FOV are arranged in a coplanar relationship along the working range of said PLIIM based camera system so that the PLIB illuminates primarily within said FOV of the IFD module; and
a speckle-pattern noise reduction subsystem, integrated with said PLIA, for reducing the temporal-coherence of said planar laser illumination beam (PLIB) before said PLIB illuminates a target object;
said speckle-pattern noise reduction subsystem applying a temporal intensity modulation technique during the transmission of said PLIB towards the target, so that the object is illuminated with a temporally coherent-reduced planar laser illumination beam (PLIB) and numerous substantially different time-varying speckle-noise patterns are produced at said image detection array over the photo-integration time period thereof;
whereby said numerous substantially different time-varying speckle-noise patterns are detected at said image detection array over said photo-integration time period, and said detected speckle-noise patterns are temporally averaged at said image detection array during said photo-integration time period thereof, thereby reducing the RMS power of observable speckle-noise patterns at said image detection array. - View Dependent Claims (8, 9, 10, 11, 12)
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Specification